Vehicle control system configured to recognize travel environment in which vehicle travels, and to provide drive assist

ABSTRACT

Provided is a vehicle control system capable of securing stability even in the event of a collision with a travel-path defining line such as a guardrail. The invention recognizes the travel-path defining line of a travel path from information about an area in a traveling direction of an ego vehicle, recognizes a traveling-direction virtual line extending from the ego vehicle in the traveling direction, and imparts a yaw moment control amount so that a formed angle between the traveling-direction virtual line and the travel-path defining line decreases after the ego vehicle collides with the travel-path defining line.

TECHNICAL FIELD

The invention relates to a vehicle control system configured torecognize a travel environment in which a vehicle travels, and providedrive assist.

BACKGROUND ART

Patent Document 1 discloses the technology of detecting a guardrail bymeans of a camera to avoid contact with the guardrail, and generatingyaw moment in an ego vehicle when the vehicle and the guardrail are inpredetermined positional relationship.

CITATION LIST Patent Document

Patent Document 1: Japanese Unexamined Patent Application Publication(Kokai) No. 2012-84038

SUMMARY OF INVENTION Technical Problem

It has been difficult to secure the stability of vehicle behavior byusing the conventional technology mentioned above.

It is an object of the invention to provide a vehicle control systemcapable of securing stability even in a situation where the vehiclecollides with a travel-path defining line such as a guardrail.

Solution to Problem

To accomplish the above object, the invention recognizes the travel-pathdefining line of a travel path from information about an area in thetraveling direction of the ego vehicle and imparts yaw moment controlamount to reduce a formed angle between a traveling-direction virtualline and a travel-path defining line after the ego vehicle collides withthe travel-path defining line.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configuration view showing a vehicle controlsystem of an Embodiment 1.

FIG. 2 is a control block diagram of an electronic control unit of theEmbodiment 1.

FIG. 3 is a block diagram showing a configuration of a travelenvironment recognition system of the Embodiment 1.

FIG. 4 is a flowchart showing image processing in the travel environmentrecognition system of the Embodiment 1.

FIG. 5 is a diagrammatic illustration schematically showing a roadembankment with steep slope areas.

FIG. 6 is an image taken schematically showing a screen image of a roadembankment with steep slope areas, which is taken from an ego vehicle.

FIG. 7 is a schematic view showing characteristic points captured in animage at the same time when the image of an actual road is taken.

FIG. 8 is a schematic view showing image-data overlay processing in theEmbodiment 1.

FIG. 9 is a pattern diagram showing a result of recognition obtained bytaking an image of a road embankment, in a direction across the road.

FIG. 10 is a diagrammatic illustration schematically showing a roadembankment with moderate slope areas.

FIG. 11 is an image schematically showing a screen image of a roadembankment with moderate slope areas, which is taken from the egovehicle.

FIG. 12 is a pattern diagram showing a result of recognition obtained bytaking an image of a road embankment, in a direction across the road.

FIG. 13 is a flowchart showing processing for judging whether vehicleattitude stabilizing control is necessary, which is executed by theelectronic control unit of the Embodiment 1.

FIG. 14 is a pattern diagram showing the ego vehicle turning toward atravel-path defining line.

FIG. 15 is a pattern diagram showing the ego vehicle traveling on acurved roadway and turning in a direction away from the travel-pathdefining line.

FIG. 16 is a flowchart showing vehicle attitude stabilizing controlprocessing of the Embodiment 1.

FIG. 17 is a flowchart showing the vehicle attitude stabilizing controlprocessing of the Embodiment 1.

FIG. 18 is a pattern diagram showing relationship between an evaluationfunction Ho(t) and a predetermined value δ according to the Embodiment1.

FIG. 19 is a schematic explanatory view showing relationship of brakingforces applied to suppress the turn of the vehicle when the vehicle isturning at a predetermined or higher vehicle speed according to theEmbodiment 1.

FIG. 20 is a timeline chart of a situation where the vehicle attitudestabilizing control processing is executed on a straight roadwayaccording to the Embodiment 1.

FIG. 21 is a timeline chart showing an operation of the vehicle attitudestabilizing control processing which is executed on a curved roadway ata predetermined or higher vehicle speed according to the Embodiment 1.

FIG. 22 is a flowchart showing contents of collision control accordingto the Embodiment 1.

FIG. 23 is a flowchart showing contents of automatic steering controlprocessing which is executed during the collision control of theEmbodiment 1.

FIG. 24 is a map showing relative positions of the collision control andvehicle attitude stabilizing control of the Embodiment 1 andconventional lane keeping control.

DESCRIPTION OF EMBODIMENTS

[Embodiment 1]

FIG. 1 is a schematic configuration view showing a vehicle controlsystem of an Embodiment 1.

A vehicle of the Embodiment 1 includes a travel environment recognitionsystem 1, an electrically-assisted power steering 2, a hydraulic brakeunit 3, a brake booster 4, a steering wheel 5, a front left wheel 6, afront right wheel 7, a rear left wheel 8, a rear right wheel 9, anelectronic control unit 10, and a vehicle motion detector 11.

The travel environment recognition system 1 takes an image of a viewahead of an ego vehicle by using stereo cameras 310 a and 310 b placedin a substantially middle position in the vicinity of a rearview mirrorlocated in an upper front portion in an interior of the ego vehicle, andcreates travel environment data.

The electrically-assisted power steering 2 calculates an assist torqueon the basis of a command according to a driver steering torque and asteering angle or steering angle speed of the steering wheel 5, assiststhe steering torque by means of an electric motor, and turns the frontright and left wheels 6 and 7. The electrically-assisted power steering2 further executes steering-torque assist control which applies yawmoment to a vehicle through after-mentioned vehicle attitude stabilizingcontrol. It is possible to employ a steer-by-wire system capable ofturning the front right and left wheels 6 and 7 independently of adriver's steering wheel operation. There is no particular limitation.

The hydraulic brake unit 3 independently controls wheel-cylinderpressure which applies a braking torque to the four wheels according toa driver's brake operation force or a state of the vehicle. Thehydraulic brake unit 3 may be a VDC unit which carries out vehiclebehavior control, such as vehicle dynamics control and vehicle stabilitycontrol, which are conventional controls. Alternatively, the hydraulicbrake unit 3 may be a unique hydraulic unit. There is no particularlimitation.

The brake booster 4 is a booster which boosts a driver's brake pedalforce with respect to a piston in a master cylinder, which is activatedby the brake pedal, and thus electrically assists a stroke force of thepiston. Master-cylinder pressure is generated by the force boosted bythe brake booster 4, and outputted to the hydraulic brake unit 3. Thebrake booster 4 does not have to be configured to electrically assistthe force, and may be a negative-pressure booster using negativepressure of an engine. There is no particular limitation.

The vehicle motion detector 11 detects the speed of vehicle (vehiclespeed), longitudinal acceleration, lateral acceleration, yaw rate,steering angle, steering torque, and the like.

The electronic control unit 10 controls the travel environmentrecognition system 1, the electrically-assisted power steering 2, andthe hydraulic brake unit 3 in accordance with detection values of thevehicle motion detector 11. When a travel-path defining line whichdefines a travel path on a road recognized from an image taken by thetravel environment recognition system 1 and a traveling direction of theego vehicle (traveling-direction virtual line extending from the egovehicle in the traveling direction, for example) intersect with eachother, the electronic control unit 10 activates theelectrically-assisted power steering 2 and/or the hydraulic brake unit3, and applies the yaw moment and/or deceleration to the vehicle, tothereby carry out the vehicle attitude stabilizing control so that thetraveling direction of the vehicle and a traffic lane are parallel toeach other. The “travel-path defining line” here means a center line, atraffic lane line if white lines are recognized, a line connectingpositions where guardrails are installed if guardrails are recognized, aline or the like indicating a boundary between a flat area and a slopearea of a road embankment (hereinafter, also simply referred to as a“road edge”). The vehicle attitude stabilizing control will be laterdescribed in details.

If driven by the driver's brake operation force, the hydraulic brakeunit 3 applies equal braking forces to the front right and left wheels 6and 7 and to the rear right and left wheels 8 and 9. According to thevehicle attitude stabilizing control, right and left braking forces aregenerated while the braking forces are differentiated between the frontright and left wheels 6 and 7 and between the rear right and left wheels8 and 9, to thereby apply the yaw moment to the vehicle.

(Vehicle Attitude Stabilizing Control System)

FIG. 2 is a control block diagram of an electronic control unit 10 ofthe Embodiment 1. The electronic control unit 10 includes adeparture-tendency calculating unit 20 and a vehicle attitudestabilizing control unit 21. The departure-tendency calculating unit 20calculates a lane departure tendency of a vehicle. The vehicle attitudestabilizing control unit 21 activates the electrically-assisted powersteering 2 and/or the hydraulic brake unit 3 when the departure-tendencycalculating unit 20 detects the departure tendency of the vehicle fromthe driving lane. The vehicle attitude stabilizing control unit 21 thusapplies a yaw moment and/or deceleration to the vehicle to suppress thedeparture tendency. The vehicle attitude stabilizing control unit 21makes the ego vehicle parallel to the travel-path defining line inaccordance with the traveling-direction virtual line extending from theego vehicle in the traveling direction, an angle formed by thetraveling-direction virtual line and a virtual travel-path defining linewhich is in a direction of tangent to the travel-path defining line, ata position where the traveling-direction virtual line and thetravel-path defining line intersect (hereinafter, referred to as a“formed angle θ”. See FIGS. 14 and 15), and a turning state of the egovehicle.

The departure-tendency calculating unit 20 includes a travel-pathdefining line recognition unit (road-edge line recognition unit) 22, avehicle's current position recognition unit 23, an intersect timecalculation unit 24, a virtual travel-path defining line calculationunit (virtual road-edge line recognition unit) 25, and an activationnecessity judgment unit 26.

The travel-path defining line recognition unit 22 recognizes boundarylines (including a center line) of road edges existing on right and leftsides of a traffic lane on which the ego vehicle travels, which includewhite lines, guardrails and curbs, from an image of a view ahead of theego vehicle, which is taken by the travel environment recognition system1.

The vehicle's current position recognition unit 23 recognizes a currentposition of a vehicle, which is a forward end of the vehicle as viewedin a traveling direction of the ego vehicle, and also recognizes thetraveling-direction virtual line from the vehicle's current position inthe traveling direction of the ego vehicle. The current position of thevehicle may be a substantially central position of the ego vehicle,instead of the forward end of the vehicle as viewed in the travelingdirection. If the ego-vehicle traveling direction (traveling-directionvirtual line) intersects with a travel-path defining line on the right,a right forward position of the ego vehicle may be the current positionof the vehicle. If the ego-vehicle traveling direction intersects with atravel-path defining line on the left, a left forward position of theego vehicle may be the current position of the vehicle. The currentposition of the vehicle may also be set at a position located withleeway as compared to the position of the actual end of the vehicle.There is no particular limitation.

The intersect time calculation unit 24 computes an intersect time,namely, a time period in which the ego vehicle travels at current speedfrom the vehicle's current position to an intersection of thetraveling-direction virtual line and the travel-path defining line.

The virtual travel-path defining line calculation unit 25 calculates thevirtual travel-path defining line which is in the direction of tangentto the travel-path defining line at the intersection of the travel-pathdefining line and the traveling-direction virtual line. If there are aplurality of intersections of the travel-path defining line and thetraveling-direction virtual line in the traveling direction of the egovehicle, the virtual travel-path defining line calculation unit 25calculates the virtual travel-path defining line which is in thedirection of tangent at an intersection point closest to the egovehicle.

The activation necessity judgment unit 26 makes a judgment on the basisof the intersect time as to whether the activation of the vehicleattitude stabilizing control is necessary, that is, whether controlintervention by the vehicle attitude stabilizing control should becarried out. More specifically, a judgment is made as to whether theintersect time is equal to or longer than predetermined time. If theintersect time is equal to or longer than the predetermined time, it isjudged that safety is secured, that there is no need for controlintervention, and that the vehicle attitude stabilizing control isunnecessary. To the contrary, if the intersect time is shorter than thepredetermined time, it is judged that the vehicle attitude stabilizingcontrol is necessary.

If it is judged by the activation necessity judgment unit 26 that thevehicle attitude stabilizing control is necessary, the vehicle attitudestabilizing control unit 21 conducts the vehicle attitude stabilizingcontrol. If judged unnecessary, the vehicle attitude stabilizing controlis not conducted.

(Recognition of the Travel-path Defining Line)

The recognition of the travel-path defining line will be explained indetails. FIG. 3 is a block diagram showing a configuration of a travelenvironment recognition system of the Embodiment 1. The travelenvironment recognition system 1 is provided with a stereo camera 310comprising a pair of cameras 310 a and 310 b as an image-taking device,and recognizes environment around a vehicle. According to the Embodiment1, the cameras are installed at the same distance from the center of thevehicle in a vehicle-width direction. It is possible to install three ormore cameras. The description of the Embodiment 1 refers to aconfiguration in which images taken by the cameras are processed in thetravel environment recognition system 1. Image processing or the likemay be executed by another controller.

The travel environment recognition system 1 is configured to obtaindistance to an object captured in an image on the basis a triangulationprinciple using difference in vision (hereinafter, referred to as“disparity”) which occurs when an image is taken by the plurality ofcameras 310 a and 310 b. For example, a relational expression below istrue, where Z denotes distance to the object; B denotes distance betweenthe cameras; f denotes a focal length of the cameras; and δ isdisparity.Z=(B×f)/δ

The travel environment recognition system 1 includes a RAM 320 whichstores images taken, a CPU 330 which executes computational processing,a data ROM 340 which stores data, and a program ROM 350 in which arecognition processing program is stored. The stereo camera 310 is fixedto a rearview mirror portion in a vehicle interior and configured totake the image of the view ahead of the ego vehicle at a predetermineddepression angle at the fixed position. The image of the view ahead ofthe ego vehicle, which is taken by the stereo camera 310 (hereinafter,referred to as an “image taken”) is scanned into the RAM 320. The CPU330 executes the recognition processing program stored in the programROM 350 with respect to the image taken which is scanned into the RAM320, to thereby detect a traffic lane and a three dimensional objectahead of the ego vehicle, and estimate a road configuration. A result ofthe estimation by the CPU 330 (computation result) is outputted to thedata ROM 340 and/or ECU 10.

FIG. 4 is a flowchart showing image processing in the travel environmentrecognition system of the Embodiment 1.

Step 201 executes processing of inputting images taken by the camera 310a situated on the left. Data of the images taken by the camera 310 a areinputted into the RAM 320.

Step 202 executes processing of inputting images taken by the camera 310b situated on the right. Data of the images taken by the camera 310 bare inputted into the RAM 320.

In Step 203, the CPU 330 executes processing of calculatingcorresponding points captured in the images.

In Step 204, the CPU 330 executes processing of calculating distance tothe calculated corresponding points. The distance calculation processingis carried out on the basis of the relational expression, Z=(B×f)/δ.Step 205 executes processing of outputting distance information.

In Step 206, the CPU 330 makes a judgment as to presence of an imageinput signal. If there is the image input signal, the routine returns toStep 201 and repeats the present flow. If there is no image inputsignal, the routine terminates the computation processing and enters await state.

(Recognition Processing on a Road with a Steep Slope)

The following description explains image processing in a case whereoutside zones located outside a road (such as both sides of the road onwhich the ego vehicle travels) are lower than a road surface. FIG. 5 isa diagrammatic illustration schematically showing a road embankment withsteep slope areas. In this road embankment, a road is formed on an upperside portion of an embankment having a substantially trapezoidalcross-section. Between the road and the outside zone, a slope area isformed, and outside the slope area is a low area. Hereinafter, the roadis also referred to as a “road surface”. FIG. 6 is an imageschematically showing a screen image of the road embankment with steepslope areas, which is taken from the ego vehicle. In this image taken,the road edge which is the travel-path defining line and the outsideareas (zones lower than the road surface) are in abutment with eachother in the image taken. In the case of this road, the slope has anangle larger than the depression angle of the stereo camera 310 (slopeis steep), so that a dead zone (portion which is not captured in animage) is created, and the slope area is not captured on a screen. Asthe result, the road edge and the low areas are in abutment with eachother in the image taken. To solve this, a road zone and another zoneindicating the low area are detected on the screen, and among boundariesbetween these zones on the screen, a road side is extracted as an actualroad edge, to thereby achieve detection reflecting an actual roadenvironment.

(Improvement of Accuracy in Image Processing)

If the road and the outside zones are visually completely homogenous, itis difficult to extract a certain place in the same zone in images takenby the two cameras. FIG. 7 is a diagrammatic illustration showingcharacteristic points captured in an image at the same time the image ofan actual road is taken. As illustrated in FIG. 7, in many places on theactual road, there are visually characteristic points throughout theroad including particles of asphalt concrete used to surface roads, roadmarkings, joints and cracks in asphalt, tire marks left by travelingvehicles, and also tracks even in unsurfaced roads. In the zones lowerthan the road, characteristic points such as weeds are throughout thezone. In other words, there is a visual difference between the roadsurface provided with surfacing or land adjustment for the traveling ofvehicles and the zones lower than the road surface, which are notprovided with such treatment. A boundary portion between the roadsurface and the lower zone is highly likely to be visuallycharacteristic.

Since there are many visually characteristic points on the road, theoutside areas, and the boundaries therebetween, it is possible to make acomparison of these zones with one another within the images taken bythe cameras 310 a and 310 b, calculate a direction and distance from thecameras 310 a and 310 b, and find a position of each characteristicpoint. This makes it possible to understand that an aggregate of thecharacteristic points on the road lies in substantially the same planeand that the characteristic points on the areas lower than the road arelocated on the outside zones.

(Overlay Processing)

Concerning a road surface configuration, a characteristic point on thescreen, such as not only a road marking but a small crack and a tiremark on the road, is extracted from the images of the view ahead of theego vehicle, which are taken by the stereo camera 310. On the basis of aposition gap of the images taken by the two cameras on the screen,distance to the point is measured. On the other hand, characteristicpoints do not always evenly exist on the entire road surface. Even ifthey do exist, it is unsure whether the characteristic points can bedetected all the time. Also in the zones lower than the road surface,the characteristic points are not necessarily detectable in every placeof the zones. It is then required to further improve accuracy. To thatend, the obtained distance data are accumulated in the data ROM 340 andoverlaid on data obtained from the image taken with a subsequent orlater timing.

FIG. 8 is a diagrammatic illustration showing the image-data overlayprocessing in the Embodiment 1. For example, a portion recognizable fromthe image previously taken is overlaid on a portion recognizable fromthe image taken this time. If there is a place about which distanceinformation cannot be obtained from the image previously taken, it ispossible to improve accuracy in detection of roads and environment byoverlaying the distance information newly obtained from the image takenthis time. As illustrated in FIG. 8, even if the ego vehicle istraveling, and the images obtained vary over time, a plurality of imagesare of the same zone if image-taking intervals are short because traveldistance is short due to the vehicle speed. It is therefore onlyrequired to overlay the zones of the same zone on each other. Overlayingis not limited to two images. It is effective to overlay as many imagesas possible on one another.

If the images taken have different distance data with respect to aposition recognized as the same place, priority may be given to newerdata. The use of the newer data improves accuracy in recognition. Anaverage of a plurality of data may also be used. This eliminates aneffect of disturbance included in the data and the like, and stabilizesthe recognition. It is also possible to extract data which does not muchvary from other proximate data. This enables computation based on stabledata and improvement in recognition accuracy. There are various methodsof processing as described above. It is possible to combine the methodsor employ any one of the methods.

(Road Edge Recognition Processing)

FIG. 9 is a pattern diagram showing a result of recognition obtained bytaking an image of a road embankment, as viewed in a direction acrossthe road. In this case, the slope area is steep and out of the cameraview. The slope area is therefore not captured in the image taken. Inthe screen image, it looks as if the road area and the area lower thanthe road directly abut on each other. In fact, however, a point 601 ofthe road edge and a point 602 of the outside area, which are in abutmentwith each other on the screen, do not abut on each other but areactually slightly separated from each other as illustrated in FIG. 9. Tooutput that the point of the road edge is the position of the point 602is inaccurate, so that the point 601 is outputted as the point of theroad edge.

Referring to FIG. 9, let us assume that the data of the positioncorresponding to the point 601 is not detected, and for example, a point603 located further on the inner side of the road than the point 601 isdetected to be an endmost point among points existing on the roadsurface. In this case, an area between the zone corresponding to thepoint 602 and the zone corresponding to the point 603 is a zone which isnot captured in the image also on the screen. It is then unclear as towhere in the area between the zones the road edge is located. At thesame time, since the point 602 located in the area lower than the roadsurface is observable, it can be inferred that no road exists in adirection looking down at the point 602 from the stereo camera 310. Itcan be therefore inferred that the road edge exists at least in the zonebetween the point 603 and the point 601 which is not detected in thiscase. For this reason, the position located between the points 603 and602 and closer to the road than the position corresponding to theboundary portion is outputted as the road edge.

(Road Edge Recognition Processing on a Road with a Moderate Slope)

FIG. 10 is a diagrammatic illustration schematically showing a roadembankment with moderate slope areas. In this road embankment, a road isformed in an upper portion of an embankment having a substantiallytrapezoidal cross-section. Between the road and the outside zone, aslope area is formed, and outside the slope area is a low area. FIG. 11is an image schematically showing a screen image of a road embankmentwith moderate slope areas, which is taken from the ego vehicle. In thisimage taken, the road edge and each of the slope areas are captured inthe image so as to be in abutment with each other, and the slope areasand the outside area (zone lower than the road surface) are captured inthe image so as to be in abutment with each other. In the case of thisroad, the slope has an angle smaller than the depression angle of thestereo camera 310 (slope is moderate), so that a dead zone (zone whichis not captured in an image) is not created.

FIG. 12 is a pattern diagram showing a result of recognition obtained bytaking an image of a road embankment with moderate slopes, as viewed ina direction across the road. In this case, the slope is moderate andcaptured in the image. In the screen image, it looks as if a road areaand a slope area are in abutment with each other, and the slope area andan area lower than the road are in abutment with each other. What isimportant here is to recognize the road edge. There is no need todistinct the slope area and the low area from each other. Therefore,points which are not located at the same level as the road surface areconsidered to be located outside the road. As the result, a point 901 isrecognized as the edge of the road zone, and a point 902 as a pointlocated closest to the road within the outside zone. It can be theninferred that the actual road edge exists between the points 901 and902.

(Improvement of Accuracy in Recognition of the Road Edge)

If the road and the outside area are connected to each other with amoderate inclination intervening therebetween, the inclined portion canbe imaged by the stereo camera 310 to obtain the distance informationthereof. This makes it possible to detect that the inclined portion is aslope area that is not suitable for a vehicle to pass along, and alsoconsider that a boundary between the inclined area and the road area isa road boundary (namely, a road edge).

Even if the zone lower than the road is considerably low and thereforeimpossible to be detected, for example, as in a case where the road isformed along a precipitous cliff or where contrast between a road and azone on the side of the road is weak, it is still possible to recognizethat the lower zone is outside the road.

Although the detected road edge is expected to be the actual edge of theroad, there actually is a gap due to a detection error. Because a roadedge has a weak base structure, it is sometimes inappropriate to drivealong the road edge. An effective way to cope with such possibilities isto output as a road edge a position located further on the inner side ofthe road than the detected road edge, as necessary. Contrary to theforegoing case, when the vehicle attitude stabilizing control system isused in combination as in the Embodiment 1, it is effective to output asa road edge a position located further on the outer side of the roadthan the road edge, as necessary, from the standpoint of prevention ofexcessive control or warning.

(Handling during Virtual-image Photographing)

The following is a case where the presence of a zone lower than a roadis extracted, and the zone is judged to be located outside the road.When there is a puddle of water in the road, and a virtual imagereflected on the puddle is detected, the virtual image is seeminglylocated lower than the road surface, so that the puddle zone is likelyto be incorrectly recognized as a zone lower than the road surface. Thevirtual image reflected on the puddle has characteristics different fromthose of a real image, and is therefore excluded in distinction fromzones which are actually lower than the road surface. To be morespecific, the characteristics are as listed below.

a) A virtual image is created by a distant object being reflected.Therefore, there is a road surface zone, which looks closer thanapparent distance of the virtual image, at a point farther than a zonein which the virtual image exists on the screen.

b) Because a water surface is not completely flat, the virtual image issometimes significantly distorted, which generates variation in distanceof the puddle zone.

c) If the water surface is unstable, the apparent position of thevirtual image varies with time.

d) It looks as if there is an object in a symmetrical position to anobject on the road, across the road surface (water surface).

e) If the virtual image is of a traveling vehicle, the image movesdespite that it is located in the zone lower than the road surface.

The virtual image has the foregoing characteristics which are highlyunlikely to be seen with real images. Detection of the foregoingcharacteristics makes it possible to determine that the image is not areal image but a virtual one.

[Vehicle Attitude Stabilizing Control]

FIG. 13 is a flowchart showing processing for judging whether vehicleattitude stabilizing control is necessary, which is executed by theelectronic control unit 10 of the Embodiment 1. While the vehicle istraveling, the processing is repeatedly executed, for example, with acomputation period of approximately 10 milliseconds.

In Step S1, the vehicle attitude stabilizing control unit 21 reads indetection values including vehicle speed, longitudinal acceleration,lateral acceleration, yaw rate, steering angle, and steering torque,received from the vehicle motion detector 11.

In Step S2, the travel-path defining line recognition unit 22 recognizesa position of the travel-path defining line from the image of the viewahead of the ego vehicle, which is received from the travel environmentrecognition system 1.

In Step S3, the vehicle's current position recognition unit 23recognizes the vehicle's current position which is the forward end ofthe vehicle as viewed in the traveling direction of the ego vehicle. Thevehicle's current position recognition unit 23 also obtains atraveling-direction virtual line extending from the ego vehicle in thetraveling direction.

In Step S4, the intersect time calculation unit 24 computes an intersecttime, namely, a time period in which the ego vehicle travels at currentspeed from the vehicle's current position to an intersection of thetraveling-direction virtual line and the travel-path defining line. Thevirtual travel-path defining line calculation unit 25 calculates avirtual travel-path defining line. The virtual travel-path defining lineis a tangent of the travel-path defining line at a point close to avehicle's estimated position. The vehicle's estimated position is, forexample, an intersection of the traveling-direction virtual line and thetravel-path defining line.

In Step S5, the activation necessity judgment unit 26 makes a judgmentas to whether the intersect time is shorter than a predetermined time.If the intersect time is shorter than the predetermined time, theroutine advances to Step S6. If the intersect time is equal to or longerthan the predetermined time, the routine ends. This is because a feelingof strangeness is given to the driver if a control amount is providedbefore the driver actually drives along the travel-path defining lineahead of the vehicle when the intersect time is longer than thepredetermined time.

In Step S6, the vehicle attitude stabilizing control unit 21 activatesthe electrically-assisted power steering 2 and/or the hydraulic brakeunit 3 according to a yaw moment control amount, applies yaw momentand/or deceleration to the vehicle, and executes the vehicle attitudestabilizing control. The vehicle attitude stabilizing control unit 21uses one or more of the detection values including the vehicle speed,longitudinal acceleration, lateral acceleration, yaw rate, steeringangle, and steering torque, which are read in at Step S1, to execute thevehicle attitude stabilizing control.

(Details of the Vehicle Attitude Stabilizing Control)

Details of the vehicle attitude stabilizing control processing will beexplained below. FIG. 14 is a pattern diagram showing the ego vehicleturning toward the travel-path defining line. FIG. 14 shows a state inwhich the ego vehicle turns in a direction toward the travel-pathdefining line while traveling on a straight roadway. A sign of a yawrate dφ/dt of the ego vehicle is defined as positive when the vehicle isturning right, negative when the vehicle is turning left, and zero whenthe vehicle is parallel to the travel-path defining line. In view ofrelationship between the yaw rate dφ/dt and the formed angle θ in thesituation illustrated in FIG. 14, the yaw rate dφ/dt changes intonegative since the vehicle is turning left, and the formed angle θ intopositive. The sign of the yaw rate dφ/dt and that of the formed angle θdisagree with each other.

FIG. 15 is a pattern diagram showing the ego vehicle traveling on acurved roadway and turning in a direction away from the travel-pathdefining line. In the situation illustrated in FIG. 15, since the travelpath curves to the right, the traveling direction (traveling-directionvirtual line) of the ego vehicle intersects with the travel-pathdefining line on the left. When the driver becomes aware of the curveand turns the steering wheel to the right, the formed angle θ changesinto positive, whereas the sign of the yaw rate dφ/dt of the ego vehicleis positive because of the right turn, which agrees with the sign of theformed angle θ. The following description explains relationship betweenthe agreement/disagreement of signs of the yaw rate dφ/dt and the formedangle θ and the control amount.

As illustrated in FIG. 14, for example, when the vehicle turns towardthe travel-path defining line while traveling straight, the vehicle ishardly in a stable attitude. In this case, yaw moment should be appliedin a direction away from the travel-path defining line. Even if thetraveling-direction virtual line and the travel-path defining lineintersect with each other on a curved roadway as illustrated in FIG. 15,it can be considered that the vehicle attitude is stable if the driveroperates the steering wheel, and the turning direction of the egovehicle is the same as the curved roadway.

It is therefore desired to impart a yaw moment control amount for makingstable (stabilizing) the vehicle attitude upon consideration of theforegoing travel motions. Relationship between the yaw rate (dφ/dt) andvehicle speed V is expressed as follows:(dφ/dt)=V/rwhere r denotes a turning radius. Therefore, the following is true:1/r=(dφ/dt)/V

where (1/r) is curvature. The curvature is a value indicative of aturning state of the vehicle, regardless of vehicle speed, and can betherefore handled in the same manner as the formed angle θ.

The evaluation function Ho(t) at a time t, which is obtained in light ofthe foregoing matters, is set as follows:Ho(t)=A{(dφ/dt)/V}(t)−Bθ(t)

where A and B are constants.

The evaluation function Ho(t) represents the yaw moment control amountwhich should be imparted according to difference between the turningcondition [A{(dφ/dt)/V}(t)] of the ego vehicle and the condition of theactual travel-path defining line. If the evaluation function Ho(t)indicates a large positive value while the vehicle is turning right, itis necessary to apply a left yaw moment. It is then required to apply abraking force to the left wheel or execute steering torque control whichfacilitates a left turn. If the evaluation function Ho(t) indicates anegative quantity with a large absolute value while the vehicle isturning left, it is necessary to apply a right yaw moment. It istherefore required to apply a braking force to the right wheel orexecute steering torque control which facilitates a right turn.

Using the evaluation function Ho(t) eliminates a feeling of strangenessbecause the value of the evaluation function Ho(t) is small, and the yawmoment control amount to be imparted is also small when the driverdrives along the travel-path defining line. If the driver drives towardthe travel-path defining line, the value of the evaluation functionHo(t) is large, and the yaw moment control amount to be imparted is alsolarge. This firmly secures the stability of the vehicle attitude.

As a comparative example to be compared with the invention according tothe Embodiment 1, the following description explains a technology ofcalculating a target yaw rate by dividing the formed angle between atravel locus along the recognized travel-path defining line and thetraveling-direction virtual line by an arrival time which is time thatelapses before arrival to the travel-path defining line. As in thecomparative example, if a value resulted from the division by thearrival time is used as the yaw moment control amount, the yaw rate isgradually corrected in the process where the vehicle approaches thetravel-path defining line. This causes the problem that it takes timeuntil a travel motion along the travel-path defining line is achieved.

According to the Embodiment 1, the yaw moment control amount is impartedaccording to the evaluation function Ho(t) based on difference betweenthe curvature (1/r) indicative of a current turning state of the vehicleand the formed angle θ. For that reason, it is output such a controlamount that the vehicle immediately becomes parallel to the travel-pathdefining line before the vehicle actually reaches the travel-pathdefining line, regardless of distance to the travel-path defining line(regardless of the intersect time). This enables highly safe control.Furthermore, since the control amount is computed using the relationshipbetween the curvature and the formed angle θ, when control is notrequired as in a situation where the vehicle travels along thetravel-path defining line, the vehicle attitude stabilizing control doesnot intervene even if the formed angle θ is created, so that the driveris not given a feeling of strangeness.

FIGS. 16 and 17 are flowcharts showing the vehicle attitude stabilizingcontrol processing of the Embodiment 1. The flow relates to controlprocessing executed by the vehicle attitude stabilizing control unit 21when it is judged that the vehicle attitude stabilizing control isnecessary in the step shown in FIG. 13, which judges the necessity ofthe vehicle attitude stabilizing control.

Step S101 computes the formed angle θ between the traveling direction ofthe ego vehicle and the travel-path defining line. More specifically,Step S101 obtains the formed angle between the traveling-directionvirtual line and the virtual travel-path defining line, which arecalculated in Steps S3 and S4 of FIG. 13.

Step S102 computes the yaw rate (dφ/dt) of the ego vehicle. The yaw ratemay be a yaw rate sensor value detected by the vehicle motion detector11. The yaw rate may be computed from vehicle speed or steering angleaccording to a vehicle motion model. There is no particular limitation.

Step S103 computes the evaluation function Ho(t) from the formed angleθ, the yaw rate (dφ/dt), and the vehicle speed V.

Step S104 makes a judgment as to whether the evaluation function Ho(t)is positive. If the evaluation function Ho(t) is positive, the routineproceeds to Step S105. If the evaluation function Ho(t) is zero orsmaller, the routine advances to Step S108.

Step S105 makes a judgment as to whether the evaluation function Ho(t)is larger than a predetermined value δ indicative of a dead band whichis set in advance, and if the evaluation function Ho(t) is larger, theroutine proceeds to Step S106. If the evaluation function Ho(t) issmaller than the predetermined value δ, the routine advances to StepS107.

Step S106 sets the control amount H(t) at a value obtained bysubtracting the predetermined value δ from the evaluation functionHo(t). FIG. 18 is a pattern diagram showing relationship between theevaluation function Ho(t) and the predetermined value δ. A value ofexcess of the evaluation function Ho(t) over the predetermined value δis computed as the control amount H(t).

Step S107 sets the control amount H(t) at zero.

Step S108 makes a judgment as to whether a value obtained by multiplyingthe evaluation function Ho(t) by minus (the evaluation function Ho(t) isa negative quantity and turns into a positive value if being multipliedby minus) is larger than the predetermined value δ. If the value islarger, the routine moves to Step S109. If the value is smaller than thepredetermined value δ, the routine proceeds to Step S110.

Step S109 sets the control amount H(t) at a value obtained by adding thepredetermined value δ to the evaluation function Ho(t).

Step S110 sets the control amount H(t) at zero.

Step S110A makes a judgment as to whether the vehicle speed is equal toor higher than predetermined vehicle speed Vo. If the vehicle speed isequal to or higher than the predetermined vehicle speed Vo, it is judgedthat the yaw moment control using a brake braking torque is effective.The routine then advances to Step S111. If the vehicle speed V is lowerthan the predetermined vehicle speed Vo, it is judged that the yawmoment control by the steering rather than the brake is effective. Theroutine then moves to Step S121.

Step S111 makes a judgment as to whether the control amount H(t) isequal to or larger than zero. If the control amount H(t) is equal to orlarger than zero, the routine proceeds to Step S112. If the controlamount H(t) is negative, the routine proceeds to Step S113.

In Step S112, it can be judged that a right turn needs to be suppressed.A right-wheel base control amount TR is thus set at zero, and aleft-wheel base control amount TL at H(t).

In Step S113, it can be judged that a left turn needs to be suppressed.The right-wheel base control amount is set at H(t), and the left-wheelbase control amount TL at zero.

Step S114 calculates the braking torque with respect to each wheelaccording to the following relational expressions.Front-right wheel braking torque TFR=TR×αRear-right wheel braking torque TRR=TR−TFRFront-left wheel braking torque TFL=TL×αRear-left wheel braking torque TRL=TL−TFL

where α is a constant and a value that is set according to brake forcedistribution to the front and rear wheels.

Step S115 calculates a wheel-cylinder hydraulic pressure of each wheelaccording to the following relational expressions.Front-right wheel cylinder hydraulic pressure PFR=K×TFRFront-left wheel cylinder hydraulic pressure PFL=K×TFLRear-right wheel cylinder hydraulic pressure PRR=L×TRRRear-left wheel cylinder hydraulic pressure PRL=L×TRL

where K and L are constants and conversion constants for convertingtorque into hydraulic pressure.

Step S121 makes a judgment as to whether the vehicle is in a regulartravel motion. If it is judged that the vehicle is in the regular travelmotion, the routine proceeds to Step S122. In cases other than theforegoing state (post-collision state, spinning state, a state where thevehicle departs from the road surface), the present control flow isterminated.

Step S122 makes a judgment as to whether a hand is on the steeringwheel. If it is judged that a hand is on the steering wheel, the routineadvances to Step S125. If it is judged that no hand is on the steeringwheel, the routine moves to Step S123. Whether a hand is on the steeringwheel may be checked, for example, by analyzing inertia of the steeringwheel on the basis of resonance frequency components of a torque sensoror by providing a touch sensor or the like to the steering wheel tojudge if a hand is on the wheel.

Step S123 makes a judgment as to whether a no-hands-on-wheel timeexceeds predetermined time. If the no-hands-on-wheel time exceeds thepredetermined time, the routine moves to Step S128 where automaticcontrol release is executed. If the no-hands-on-wheel time does notexceed the predetermined time, the routine advances to Step S124 wherethe no-hands-on-wheel time is incremented. The routine then moves toStep S125. If automatic steering is allowed while no hand is on thesteering wheel, the driver might overly rely on the present controlsystem and lose attention during driving.

Step S125 makes a judgment as to whether a state in which the steeringtorque is equal to or higher than a predetermined value continues forpredetermined time. If such a state continues for the predeterminedtime, it is judged that the driver steers the vehicle with theintention, and the routine moves to Step S128 where the automaticcontrol release is carried out. When the state in which the steeringtorque is equal to or larger than the predetermined value does notcontinue for the predetermined time, namely, when the steering torque islow or not continuously applied even if high, the routine proceeds toStep S126 where a high steering torque continuation timer isincremented.

Step S127 executes semi-automatic steering control. The semi-automaticsteering control is control which carries out automatic steeringaccording to the travel motion of the vehicle, regardless of thedriver's intention, and switches the automatic steering control toregular steering assist control when the no-hands-on-wheel state isconfirmed or a high steering torque is applied in a continuous manner.According to the automatic steering control, a target steering angle andthe target yaw rate for achieving the control amount H(t) are set.Electric motor control switches from torque control for applying anassist torque to rotation angle control, and an activate command isoutputted to the electric motor so as to turn the steering wheel up tothe target steering angle according to target steering-wheel turningspeed.

FIG. 19 is a schematic explanatory view showing relationship betweenbraking forces applied to suppress the turning when the vehicle turns atpredetermined or higher vehicle speed according to the Embodiment 1.When the control amount H(t) is positive and indicates the right turnstate, it is required to apply the left yaw moment. When the controlamount H(t) is negative and indicates the left turn state, it isrequired to apply the right yaw moment. The supply of the wheel-cylinderhydraulic pressure with respect to each wheel, which is calculated inStep S115, stabilizes the vehicle attitude and promptly applies the yawmoment which makes the vehicle parallel to the travel-path definingline.

FIG. 20 is a timeline chart of a situation where the vehicle attitudestabilizing control processing is executed on a straight roadwayaccording to the Embodiment 1. FIG. 20 shows a situation where thevehicle turns left due to a disturbance, such as a crosswind, whiletraveling straight, and the formed angle is created in the left-sidetravel-path defining line.

At time t1, the left yaw rate dφ/dt is generated by crosswind, andsimultaneously, the formed angle θ starts being created in thetravel-path defining line on the left. The value of the evaluationfunction Ho(t) also starts changing. In this situation, because of theleft turn state which increases the formed angle, the sign of the yawrate dφ/dt and that of the formed angle θ disagree with each other. Theevaluation function Ho(t) changes so that the absolute value is large onthe negative side. The vehicle attitude stabilizing control is notexecuted until the absolute value becomes larger than the predeterminedvalue δ. This suppresses an excessive control intervention and thusprevents the driver from having a feeling of strangeness.

At time t2, the evaluation function Ho(t) becomes equal to or largerthan the predetermined value δ, and the control amount H(t) iscalculated. Thereafter, the right-wheel base control amount TR iscalculated, and the front right-wheel braking torque TFR and the rearright-wheel braking torque TRR are calculated. At this time, the frontleft-wheel braking torque TFL and the front left-wheel braking torqueTRL are set at zero. The vehicle is thus applied with the right yawmoment and makes a turn so that the vehicle traveling direction(traveling-direction virtual line) is parallel to the direction of thetravel-path defining line.

FIG. 21 is a timeline chart showing an active state of the vehicleattitude stabilizing control processing executed on a curved roadway atpredetermined or higher vehicle speed according to the Embodiment 1.FIG. 21 shows a situation where the driver properly operates thesteering wheel on the curved roadway and drives along the travel-pathdefining line.

At time t21, the travel-path defining line of the curved roadway appearsahead of the vehicle, and the formed angle θ starts being createdbetween the travel-path defining line and the vehicle travelingdirection (traveling-direction virtual line). At this point of time, thevehicle does not yet enter the curve, so that the driver does notoperate the steering wheel, and the yaw rate dφ/dt is not generated.Although the evaluation function Ho(t) begins indicating negativequantities, these quantities are smaller than the predetermined value δ.

At time t22, the driver operates the steering wheel to drive along thecurved roadway, the yaw rate dφ/dt then starts being generated in thevehicle. The sign of yaw rate dφ/dt agrees with that of the formed angleθ, and the absolute value of the evaluation function Ho(t) becomessmall. If the vehicle travels along the travel-path defining line, thevalue of the evaluation function Ho(t) is substantially zero, andremains within a range of plus or minus δ. The vehicle attitudestabilizing control is therefore basically not executed. It is thuspossible to avoid a feeling of strangeness which is created byunnecessary control intervention.

(Collision Control)

The following description explains collision control processing which isexecuted in a case where the travel-path defining line is formed of anobstacle such as a guardrail, and the ego vehicle collides with theobstacle. The collision control includes pre-collision control andpost-collision control which are carried out in different manners. FIG.22 is a flowchart showing contents of the collision control of theEmbodiment 1. The collision control is executed in the vehicle attitudestabilizing control unit 21. The brake control executed during thecollision control is omitted from the flowchart as it includes the samecontrol contents as the brake control executed during the vehicleattitude stabilizing control, except that the brake control executedduring the vehicle attitude stabilizing control uses a value obtained bymultiplying the control amount H(t) by a gain larger than 1.

Step S301 makes a judgment as to whether there has been a collisionjudgment. If there has been the collision judgment, the routine moves toStep S303. If there has not been a collision judgment, the routine movesto Step S302. The collision judgment determines whether the vehicle isin a pre-collision state and in a state where it is difficult to avoidthe collision, from the intersect time and a measure of the formed angleθ at the current moment.

In Step S302, the collision judgment is not made, so that the vehicleattitude stabilizing control processing is executed.

Step S303 makes a judgment as to whether there is a post-collisionjudgment. If there is the post-collision judgment, the routine advancesto Step S307. If there is not the post-collision judgment, that is,before collision, the routine proceeds to Step S304. The post-collisionjudgment determines whether the vehicle is in a state immediately beforecollision and in a state where, even if the driver takes any steeringoperation or brake operation, the vehicle collides with the travel-pathdefining line such as a guardrail substantially in the current travelstate. The Embodiment 1 starts the post-collision control before thecollision actually occurs, in order to regulate the motion of thevehicle immediately after the collision. As the result, the collisionjudgment in the case where the collision of the vehicle actually occursis made during an after-mentioned post-collision control.

Step S304 makes a judgment as to whether the control amount H(t) isequal to or larger than zero. If the control amount H(t) is equal to orlarger than zero, the routine advances to Step S306. If the controlamount H(t) is a negative quantity, the routine moves to Step S305.

Step S305 reduces left steering assist torque and increases rightsteering assist torque. This makes it easy for the driver to steer thevehicle to the right.

Step S306 reduces right steering assist torque and increases leftsteering assist torque. This makes it easy for the driver to steer thevehicle to the left. In addition to the steering control of Steps S305and S306, another control is executed, which multiplies the controlamount H(t) by a gain larger than 1 to increase an absolute value of theyaw moment control amount generated by braking.

Step S307 conducts the automatic steering control. More specifically,the target steering angle and target yaw rate for achieving the controlamount H(t) are set, and the control of the electric motor switches fromthe torque control for applying the assist torque to the rotation anglecontrol. The activate command is outputted to the electric motor so asto turn the steering wheel up to the target steering angle according tothe target turning speed. There is a case where the travel-path definingline cannot be recognized immediately after a collision, and thecalculation of the control amount H(t) is delayed. To solve this, thetraveling-direction virtual line of the post-collision state isestimated before the collision occurs, and the post-collision control isaccomplished with a higher responsiveness. Although Step S304 judgeswhether the control amount H(t) is equal to or larger than zero, andconducts the assist torque control of Steps S306 and S305, the assisttorque control of Steps S306 and 305 may be conducted when the controlamount H(t) exceeds plus or minus δ as with the case of the rotationangle control shown in FIGS. 16 and 17.

[Pre-collision Control]

If it is impossible to avoid a collision, and the collision has not yetoccurred, both the brake control and the steering control are executed.The brake control multiplies the control amount H(t) by a gain largerthan 1 to increase the absolute value of the yaw moment control amountgenerated by braking. The steering control changes the right and leftassist torque gains according to the sign of the control amount H(t).For example, if the right yaw moment is applied by the brake control,the right steering assist torque is increased, and the left steeringassist torque is reduced. This facilitates the steering to the right. Ifthe left yaw moment is applied by the brake control, the left steeringassist torque is increased, and the right steering assist torque isreduced. This facilitates the steering to the left.

[Post-collision Control]

After the collision, both the brake control and the steering control areconducted according to the control amount H(t). The brake controlmultiplies the control amount H(t) by a gain larger than 1, as withbefore the collision, to increase the absolute value of the yaw momentcontrol amount generated by braking. As the steering control, theautomatic steering (rotation angle control) which carries out forcedsteering according to the sign of the control amount H(t) is conducted.

In view of the accident cases which have previously been reported, thereare many cases in which a vehicle collides with a guardrail or the likeand swerves by the impact of the collision toward the travel-pathdefining line on the opposite side to the travel-path defining lineagainst which the vehicle collide. Such a case incurs not only asingle-vehicle accident where the vehicle simply collides with theguardrail but also a multiple-vehicle accident which involves afollowing vehicle or an oncoming vehicle travelling on the oppositelane. In this light, if the vehicle collides with the guardrail or thelike, it is preferable to maintain the vehicle parallel to the guardrailwith which the vehicle has collided, in order to safely stop the vehicleand avoid the multiple-vehicle accident at the same time.

However, when the yaw rate and the lateral acceleration wildly fluctuateas in a situation immediately after a collision, it is difficult toprecisely recognize relationship between the traveling-direction virtualline and the travel-path defining line, and it is also difficult for anaverage driver to properly operate the steering wheel. After thecollision, therefore, the steering angle is controlled through steeringcontrol so that the vehicle is forced to become parallel to thetravel-path defining line. The stereo camera 310 of the Embodiment 1 isinstalled in the interior of the vehicle and therefore unlikely to getbroken by initial collision. Thus, the system with the stereo camera 310continues to be able to be controlled after the collision. This is anadvantage over other systems with a millimeter-wave radar or the like.

FIG. 23 is a flowchart showing contents of the automatic steeringcontrol processing which is executed during the collision control of theEmbodiment 1. This control flow is carried out when Step S303 judgesthat there is a post-collision judgment. The control flow is performedwhen the vehicle is in a state immediately before a collision and isabout to collide with the travel-path defining line, such as aguardrail, substantially in a current travel state.

Step S401 calculates the traveling-direction virtual line of thepost-collision state from the travel state immediately before thecollision. For example, as shown in the schematic explanatoryillustration of FIG. 23, if the vehicle collides against a guardrail atthe formed angle θ, the vehicle caroms off the guardrail at the sameangle. Step S401 estimates the traveling-direction virtual line afterthe vehicle caroms off the guardrail.

Step S402 computes the control amount H1(t) of the post-collision state.It is envisaged that the travel-path defining line goes out of the viewof the stereo camera 310 immediately after the collision, and it islikely to take time before computing a first control amount H(t), whichdeteriorates responsiveness. To solve this, the control amount H1(t)which makes the vehicle parallel to the travel-path defining lineagainst which the vehicle has collided is previously computed using theformed angle θ between the traveling-direction virtual line of thepost-collision state, which has been estimated at Step S401, and thetravel-path defining line.

In Step S403, the electrically-assisted power steering 2 is subjected toangle control so that the turning angle is zero, that is, the steeringangle is at a neutral position. Before the collision, the vehicle issteered in a direction moving away from the travel-path defining line toavoid the collision. After the vehicle is caromed by the impact ofcollision, however, it is necessary to steer the vehicle in a directionapproaching the travel-path defining line. This is for previouslysecuring the neutral position and conducting the highly responsiveautomatic steering control after the collision.

Step S404 makes a judgment as to whether the collision has actuallyoccurred. If it is judged that the collision has actually occurred, theroutine advances to Step S405. Steps S401 and S402 are repeated untilthe collision occurs. As to whether the collision has occurred, forexample, it is possible to judge whether the collision has alreadyoccurred from a sudden change in the longitudinal acceleration detectedby the vehicle motion detector 11. It is also possible to judge that thecollision has occurred on the basis of an airbag activation signal orthe like which is installed in the vehicle. There is no particularlimitation.

Step S405 makes a judgment as to whether the control amount H(t) of thepost-collision state has been calculated. If the control amount H(t) hasnot been computed, the routine moves to Step S406, and the automaticsteering control is carried out using the control amount H1(t) which haspreviously been computed in Step S402. If the control amount H(t) afterthe collision has been calculated, the routine proceeds to Step S407where the automatic steering control using the control amount H(t) iscarried out. As described above, Steps S406 and S407 also executecontrol which multiplies the control amounts H1(t) and H(t) by a gainlarger than 1 to increase the absolute value of the yaw moment controlamount generated by braking. Control for post-collision vehicle attitudestabilization can be begun immediately before the collision, and the yawmoment control can be quickly begun even after the collision.

Concerning the calculation of the control amount H(t) after thecollision, if the ego vehicle is caromed in a large way by the impact ofcollision, it takes time before the stereo camera 310 recognizes thetravel-path defining line against which the vehicle has collided.Meanwhile, the yaw rate detected by the vehicle motion detector 11 isused to integrate the yaw rates after the collision to estimate theformed angle.

(Positioning and Technical Purposes of the Controls)

FIG. 24 is a map showing relative positions of the collision control andvehicle attitude stabilizing control of the Embodiment 1 andconventional lane keeping control. A horizontal axis indicates theintersect time, and the vertical axis the formed angle θ. A controllimit line represents, for example, a limitation associated with arecognition limit of the stereo camera, a limitation associated with thefact that the driver is given a feeling of strangeness, in spite of asufficient intersect time, when the yaw moment control amount requiredto solve the formed angle θ is imparted, and a limitation associatedwith the fact that the yaw moment cannot be achieved within theintersect time even if the maximum yaw moment control amount isimparted. The lane keeping control explained here means control whichapplies the yaw moment according to the intersect time with thetravel-path defining line and the formed angle θ to suppress departurefrom the travel-path defining line.

As illustrated in FIG. 24, the conventional lane keeping control, forexample, imparts a control amount applicable in an area where the formedangle θ rises up to approximately 5 degrees. This makes it possible toprevent or suppress lane departure without giving a feeling ofstrangeness to the driver. If a large control amount required in areasother than the lane keeping control area is outputted, the driver mightbe given a feeling of strangeness. Therefore, for example, only warningis applied.

If the travel-path defining line is a traffic lane, and the vehiclemerely crosses the lane as the result of negligent driving, that doesnot directly incur an accident or the like. It is then only required toconduct the lane keeping control which previously imparts a small yawmoment control amount. If the travel-path defining line is not a trafficlane but an obstacle, such as a guardrail and a sound abatement shield,or if there is a steep slope outside the road, the securing of safety ismore important than the prevention of feeling of strangeness. Accordingto the Embodiment 1, in an area where the formed angle θ exceeds thelane keeping control area, so that a large yaw moment control amount isrequired to be imparted, a vehicle attitude stabilizing control area isset, and a relatively large yaw moment control amount is imparted at anearly stage, regardless of the intersect time.

In an area where the intersect time is shorter or the formed angle θ islarger, as compared to the vehicle attitude stabilizing control area,the avoidance of collision is considered to be difficult. In such acase, a braking torque and a cornering force are created using a controlamount which is much larger than the control amount imparted during thevehicle attitude stabilizing control, for example, up to the vicinity ofa performance limit of friction circle of a tire. After the collision,the steering control is executed to make the vehicle parallel to thetravel-path defining line in a forced manner to some degree in light ofavoidance of a multiple-vehicle accident, which further secures safety.

As described above, the Embodiment 1 provides the operation andadvantages listed below.

(1) The vehicle control system includes the travel-path defining linerecognition unit 22 (travel-path defining line recognition unit)configured to recognize the travel-path defining line of the travel pathfrom information about an area in the traveling direction of the egovehicle;

the vehicle's current position recognition unit 23 (traveling-directionvirtual line recognition unit) configured to recognize thetraveling-direction virtual line extending from the ego vehicle in thetraveling direction;

Steps S301 and S303 (collision judgment unit) configured to make ajudgment as to whether the ego vehicle has collided with the travel-pathdefining line; and

the collision control flow (collision control unit) configured to impartthe control amount H(t) (yaw moment control amount) so that the formedangle θ between the traveling-direction virtual line and the travel-pathdefining line decreases after the ego vehicle collides with thetravel-path defining line.

After the collision, even if the vehicle attitude is likely to beunstable, it is possible to output the control amount which quicklymakes the vehicle parallel to the travel-path defining line, whichenables highly safe control.

(2) Step S401 (collision control unit) estimates the traveling-directionvirtual line of the post-collision state, and calculates the controlamount H1(t) on the basis of the traveling-direction virtual lineestimated in Step S402, before the collision.

For example, even if the vehicle collides with and caroms off aguardrail, and the travel-path defining line cannot be recognized, theyaw moment control amount can be imparted according to the controlamount H1(t) estimated before the collision. This enables highly safecontrol.

(3) Step S404 (collision judgment unit) makes a judgment as to whether acollision has occurred, on the basis of change amount of longitudinalacceleration of the vehicle.

This makes it possible to accurately detect a time point when thecollision has actually occurred, and properly achieve the switching ofcontrols before and after the collision, and the like.

(4) Step S403 (collision control unit) estimates the traveling-directionvirtual line of the post-collision state before the collision, andstarts controlling the turning angle before the collision on the basisof the estimated traveling-direction virtual line.

More specifically, because of the control which returns the steeringangle to the neutral position before the collision or previously appliessome countersteer before the collision, for achieving the yaw momentcontrol amount required after the collision highly responsively, it ispossible to output such a control amount that the vehicle more quicklybecomes parallel to the travel-path defining line of the post-collisionstate.

(5) Steps S405, S406 and S407 (collision control unit) impart the yawmoment control amount, regardless of the steering operation of thedriver.

When the yaw rate and the lateral acceleration wildly fluctuate as in asituation immediately after a collision, it is difficult to preciselyrecognize the relationship between the traveling-direction virtual lineand the travel-path defining line, and it is also difficult for anaverage driver to properly operate the steering wheel. After thecollision, therefore, the steering angle is controlled by the steeringcontrol so that the vehicle is forced to become parallel to thetravel-path defining line, which ensures higher safety.

(6) There is provided the vehicle motion detector 11 (yaw rate detectionunit) configured to detect the yaw rate of the vehicle; and

Step S405 (collision control unit) calculates the formed angle θ of thepost-collision state on the basis of an integrated value of the detectedyaw rate, and imparts the yaw moment control amount.

If the ego vehicle is caromed in a large way by the impact of collision,it takes time before the stereo camera 310 recognizes the travel-pathdefining line against which the vehicle has collided. The calculation ofthe control amount thus tends to be delayed. However, since the formedangle θ is calculated on the basis of the yaw rate, the control amountH(t) can be quickly calculated.

(7) There is provided the electrically-assisted power steering 2(steering actuator) configured to control the steering torque applied bythe driver; and

Steps S305 and S306 (collision control unit) differentiate the steeringtorque between the right and the left steering so that the formed angleθ decreases before the collision.

This makes it possible to guide the vehicle into the steering statewhere the vehicle becomes further parallel to the travel-path definingline while allowing the driver to steer the vehicle, and secure safetywithout giving a feeling of strangeness to the driver. To carry out theautomatic steering (S307), the electrically-assisted power steering 2 isswitched from the torque control to the rotation angle control toachieve the turning angle and yaw rate as desired.

The Embodiment 1 is provided with the electrically-assisted powersteering 2. If the vehicle is installed with a steer-by-wire system,however, automatic control can be carried out on a turning actuatorside, regardless of the steering operation of the driver. It is alsopossible to conduct control of a reaction motor to guide the formationof a necessary steering angle. There is no particular limitation.

(8) Steps S405 to S407 (collision control unit) automatically controlthe electrically-assisted power steering 2 (steering actuator) so thatthe formed angle θ decreases after the collision.

When the yaw rate and the lateral acceleration wildly fluctuate as in asituation immediately after a collision, it is difficult to preciselyrecognize the relationship between the traveling-direction virtual lineand the travel-path defining line, and it is also difficult for anaverage driver to properly operate the steering wheel. After thecollision, therefore, the steering angle is controlled through thesteering control (rotation angle control) so that the vehicle is forcedto become parallel to the travel-path defining line, which ensureshigher safety.

(9) The collision control further imparts the yaw moment control amountby executing the brake control which applies the braking torque to thewheels.

This makes it possible to impart the yaw moment control amount to thevehicle simultaneously with deceleration and thus improve safety.

(10) There is provided the electrically-assisted power steering 2(turning actuator) configured to control the turning angle of a steeredwheel; and before the collision, the collision control controls thesteered wheel to such a turning angle that the yaw moment control amountrequired after the collision is easily outputted.

To be more specific, because of the control which returns the steeringangle to the neutral position before the collision or previously appliessome countersteer before the collision, for achieving the yaw momentcontrol amount required after the collision highly responsively, it ispossible to output such a control amount that the vehicle more quicklybecomes parallel to the travel-path defining line even after thecollision.

(11) The travel-path defining line recognition unit 22 is the stereocamera configured to measure distance by using the disparity generatedwhen the plurality of cameras 310 a and 310 b take an image of the sameobject.

This makes it possible to stereoscopically grasp the distance ahead ofthe vehicle and an obstacle located ahead of the vehicle, and set acontrol gain which differs between an obstacle, such as a guardrail, anda white line. In this case, the gain is set larger if there is thepossibility of a collision against the obstacle, so that highly safecontrol can be achieved.

(12) The collision control unit imparts the yaw moment control amountaccording to an intersection angle which is difference between theformed angle between the traveling-direction virtual line and thetravel-path defining line, and the curvature according to the turningradius of the ego vehicle.

This makes it possible to output such a control amount that the vehiclequickly becomes parallel to the travel-path defining line before thevehicle actually reaches the travel-path defining line, regardless ofdistance from the ego vehicle to the travel-path defining line, so thathighly safe control can be achieved. Furthermore, the control amount iscomputed using the relationship between the curvature and the formedangle θ. Therefore, when control is unnecessary as in a situation wherethe vehicle travels along the travel-path defining line, the collisioncontrol does not intervene even if the formed angle θ is generated. Thedriver is therefore not given a feeling of strangeness.

(13) There is provided a steering actuator 2 configured to control thesteering torque applied by the driver. The collision control units S305and S306, before the collision, differentiate the steering torquebetween the right and the left steering so that the formed angledecreases, and impart the yaw moment control amount so that the formedangle decreases by executing the brake control which applies the brakingtorque to the wheels.

This makes it possible to guide the vehicle into such a steering statethat the vehicle becomes parallel to the travel-path defining line whileallowing the steering operation of the driver, and ensure safety withoutgiving the feeling of strangeness to the driver. It is also possible toimpart the yaw moment control amount to the vehicle along withdeceleration, which improves safety.

(14) There is provided the steering actuator 2 configured to control thesteering torque applied by the driver. The collision control units S405to S407, after the collision, automatically control the steeringactuator so that the formed angle decreases, and impart the yaw momentcontrol amount so that the formed angle decreases by executing the brakecontrol which applies the braking torque to the wheels.

After the collision, the steering angle is controlled so that thevehicle is forcibly made parallel to the travel-path defining linethrough the steering control (rotation angle control), so that highersafety can be secured. At the same time, the yaw moment control amountcan be applied to the vehicle along with deceleration, which improvessafety.

The above-described embodiment makes it possible to output such acontrol amount that the vehicle becomes parallel to the travel-pathdefining line of the post-collision state even if the vehicle attitudeis likely to be unstable, and achieve highly safe control.

The foregoing description merely explains several embodiments of theinvention. Those skilled in the art could easily understand that theembodiments described above may be changed or modified in various wayswithout substantially deviating from new teachings and advantages of theinvention. Therefore, it is intended to include within the technologicalscope of the invention all aspects added with such changes ormodifications.

The present patent application claims priority to Japanese PatentApplication No. 2013-116320 filed on May 31, 2013. The entire disclosureof Japanese Patent Application No. 2013-116320 filed on May 31, 2013including description, claims, drawings and abstract is incorporatedherein by reference in its entirety.

The entire disclosure of Japanese Unexamined Patent ApplicationPublication No. 2012-84038 (Patent Document 1) including description,claims, drawings and abstract is incorporated herein by reference in itsentirety.

REFERENCE SIGNS LIST

1 travel environment recognition system

2 electrically-assisted power steering

3 hydraulic brake unit

4 brake booster

5 steering wheel

10 electronic control unit

11 vehicle motion detector

20 departure-tendency calculating unit

21 vehicle attitude stabilizing control unit

22 travel-path defining line recognition unit

24 intersect time calculation unit

25 virtual travel-path defining line calculation unit

26 activation necessity judgment unit

310 stereo camera

The invention claimed is:
 1. A vehicle control system comprising: an electronic control unit configured to: recognize a travel-path defining line of a travel path from information about an area in a traveling direction of a vehicle to which the vehicle control system is mounted; recognize a traveling-direction virtual line extending from the vehicle in the traveling direction; make a judgment as to whether the vehicle has collided with an obstacle corresponding to the travel-path defining line; and estimate the traveling-direction virtual line of a post-collision state before a collision, and impart a yaw moment control amount on the basis of the estimated traveling-direction virtual line so that a formed angle between the estimated traveling-direction virtual line and the travel-path defining line decreases after the vehicle collides with the obstacle.
 2. The vehicle control system of claim 1, wherein: the electronic control unit is configured to make a judgment as to whether a collision has occurred, on the basis of a change amount of longitudinal acceleration of the vehicle.
 3. The vehicle control system of claim 1, wherein: the electronic control unit is configured to estimate the traveling-direction virtual line of the post-collision state before the collision, and start controlling a turning angle before the collision on the basis of the estimated traveling-direction virtual line.
 4. The vehicle control system of claim 1, wherein: the electronic control unit is configured to impart the yaw moment control amount, regardless of a steering operation of a driver.
 5. The vehicle control system of claim 1, comprising: a yaw rate sensor configured to detect a yaw rate of the vehicle, wherein: the electronic control unit is configured to calculate the formed angle of the post-collision state on the basis of an integrated value of the detected yaw rate, and impart the yaw moment control amount.
 6. The vehicle control system of claim 1, comprising: a steering actuator configured to control a steering torque applied by a driver, wherein: the electronic control unit is configured to differentiate the steering torque between right and left steering before the collision so that the formed angle decreases.
 7. The vehicle control system of claim 6, wherein: the electronic control unit is configured to automatically control the steering actuator after the collision so that the formed angle decreases.
 8. The vehicle control system of claim 1, wherein: the electronic control unit is configured to impart the yaw moment control amount by executing brake control which applies a braking torque to wheels.
 9. The vehicle control system of claim 1, comprising: a turning actuator configured to control a turning angle of a steered wheel, wherein: the electronic control unit, before the collision, is configured to estimate the traveling-direction virtual line of the post-collision state, impart the yaw moment control amount so that the formed angle between the traveling-direction virtual line and the travel-path defining line decreases on the basis of the estimated traveling-direction virtual line after the vehicle collides with the obstacle, and before the collision, control the steered wheel to a turning angle formed in a direction returning the steered wheel to a neutral direction where the yaw moment control amount required after the collision is easily outputted.
 10. The vehicle control system of claim 1, wherein: the electronic control unit is configured to recognize the travel-path defining line based on an image obtained by a stereo camera.
 11. The vehicle control system of claim 1, wherein: when a time to an intersection point of the travel-path defining line and the traveling-direction virtual line is shorter than a predetermined time, the electronic control unit is configured to impart the yaw moment control amount based on an evaluation function using the formed angle between the traveling-direction virtual line and the travel-path defining line, and a curvature according to a turning radius of the vehicle.
 12. The vehicle control system of claim 1, comprising: a steering actuator configured to control a steering torque applied by a driver, wherein: the electronic control unit, before the collision, is configured to differentiate the steering torque between right and left steering so that the formed angle decreases, and impart the yaw moment control amount so that the formed angle decreases by executing brake control which applies a braking torque to wheels.
 13. The vehicle control system of claim 1, comprising: a steering actuator configured to control a steering torque applied by a driver, wherein: the electronic control unit, after the collision, is configured to automatically control the steering actuator so that the formed angle decreases, and impart the yaw moment control amount so that the formed angle decreases by executing brake control which applies a braking torque to wheels. 